COMBINED DETECTION OF ELECTROMAGNETIC AND ACOUSTIC EMISSIONS ASSOCIATED WITH ROCK FAILURE

Abstract

We describe investigations of acoustic and electromagnetic emissions in rocks under pressure. Their combined use provides quantitative measures of the stress state of the rock body and makes it possible to study the development of geomechanical processes and to improve rock monitoring. We tested specimens of coal, claystone, sandstone, granite, marble and limestone. The investigations included mechanical tests of cubic specimens measuring 40 mm on a side. During the experiments, acoustic emissions and electromagnetic radiation resulting from the formation and expansion of cracks were recorded. Several phenomena were identified during the investigation: a local increase in the amplitude of acoustic and electromagnetic pulses indicating imminent attainment of the specimen's ultimate strength and the onset of the declining transcritical branch of the stress-strain diagram, an increase in the number of pulses of both types of radiation, and their simultaneous occurrence. Statistical analysis of the data revealed a correlation between the total number of electromagnetic pulses and the strength of the rock under uniaxial compression. The results indicate that it is possible to use the characteristics of acoustic emissions and electromagnetic radiation in combination to improve monitoring of the stress state of burst-prone coal seams near the workface.